Like Burrito Bunny said, unfortunately since people have already posted to your topic you can not delete it, however, like they said, you can still ask to get your topic locked by reporting it and asking for it to be locked; you can report your topic to the moderators by clicking the small white triangle at the top of your post with the red "!" in it. For your report message say something under the lines of, "Can I please have my topic locked? Thank you!" and a moderator will be more then happy to lock your topic for you.